The invention relates to a camshaft adjuster for internal combustion engines.
Camshaft adjusters are known in the form of piston-type adjusters with an axially displaceable piston (DE 40 29 849 C2, DE 196 11 365 A1 and DE 197 26 300 A1) and in the form of vane-type adjusters with vanes that can be acted upon and pivoted in the circumferential direction. In connection with both designs, the camshaft adjuster is fixed as an end-mounted extension of the camshaft by means of a central clamping screw.
For the purpose of controlling the hydraulic pressure supply to the camshaft adjuster, DE 40 29 849 C2 discloses the provision of an external 4/2-way valve, from which supply passages run to the camshaft and to the actuating piston that is provided here as the actuating means and is arranged in an accommodation space between the inner element and the outer element, the drive connection to the crankshaft running via the outer element.
The long conduit paths that this entails, with the risk of corresponding leaks and of a certain elasticity, can have the effect that the system has inadequate hydraulic rigidity and thus makes satisfactory control more difficult, not to mention the fact that the external arrangement of the control device formed by the directional control valve has a negative effect in terms of the outlay on construction and the size of the installation space required.
DE 196 11 365 A1 discloses integration of the control device designed as a multi-way valve into the clamping screw. The result is that the latter acts as a housing to form an axial receptacle for a centrally situated and axially displaceable control spool via which pressure medium can be supplied to the actuating means radially along short paths.
In view of this, provision is made to guide the camshaft adjuster""s inner element, which is fixed in terms of rotation relative to the camshaft, the camshaft adjuster""s outer element, which can be turned relative to the inner element and via which the drive connection to the crankshaft runs, on the clamping screw, irrespective of centering of the inner element relative to the camshaft independently of this. This requires very narrow tolerances, that is to say a high outlay on manufacture, and furthermore leads to misalignment errors due to the cumulative effect of a number of radial guides subject to play, these errors potentially having disadvantageous effects on concentricity of running and vibration, such concentricity and misalignment errors also make it more difficult to operate the control spool by means of the axially offset actuating magnet as actuator, associated with the spool on the housing side, with the minimum clearance relative to the armature carried by the control spool. However, larger clearances lead to a need for more power and hence for more space, and, given the conditions of construction in the case of internal combustion engines for motor vehicles, this is often not available, if only because of the axial extension entailed by the camshaft adjuster.
The object of the present invention is to construct a camshaft adjuster of the type stated at the outset in such a way that optimum centering of the camshaft adjuster is achieved. This centering simultaneously creates the conditions for particularly simple and economical manufacture.
According to the invention, this is achieved by the clamping screw forming the element of the camshaft adjuster that effects centering relative to the camshaft, eliminating the need to provide the adjuster with any further centering support as regards its inner and outer element and its lateral closure elements in the form of covers. This eliminates the need for axial undercuts or projections on the inner and outer elements, which would make manufacture more difficult. Moreover, the configuration according to the invention, involving centering of the entire camshaft adjuster, including the connection of the control device formed by the multi-way valve to the actuator, by means of the clamping screw, creates particularly favorable conditions for largely tolerance-free centering without excessive demands as to manufacture, with ideal conditions for optimum, vibration-free concentricity of running and with the minimum required clearances at the transition between the control spool and the actuator.
As a refinement of the invention, the inner element and the outer element can be designed with flat end faces, that is to say form disc-shaped elements, which are covered over a certain area by annular covers, with the result that the covers require only axial clamping. It has proven expedient here if the covers adjoin the centering collar of the camshaft radially on the inside, providing sufficient radial overlap with the inner and outer elements to allow the use of simple sealing means in so far as these are to be used, the precise centering with small clearances achieved by means of the invention also having an advantageous effect as regards the reduction of leakage.
The refinement according to the invention of using disc-shaped inner and outer elements and covers leads to particularly far-reaching simplifications in the case of camshaft adjusters designed as vane-type adjusters.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.